1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly to an apparatus and method for transmitting and receiving error check information of control information to maintain uniform reception of control information transmitted from a terminal.
2. Description of the Related Art
Typical mobile communication systems may be divided into two types according to their applications. The first type supports a voice service and the second type supports a data service. A typical mobile communication system is a Code Division Multiple Access (CDMA) system. One of the currently used CDMA system, which supports only a voice service, complies with the International Standard (IS)-95 and the IS-95 based specifications. As the communication technology has developed along with users' demands, the mobile communication system has gradually evolved to the point where it supports a high rate data service. For example, a 1st generation CDMA 2000 (CDMA 2000 1×) system was designed to simultaneously support both the voice and audio services, whereas a 1×Evolution in Data Only (EVDO) system was designed to support only the high rate data service by allocating to the data service all resources achievable by the CDMA 2000 1× system.
The mobile communication system generally performs transmission in two directions: forward and reverse. The forward direction is from a base station, which covers a predetermined area (referred to as a “cell”), to a mobile terminal capable of moving between cells. The reverse direction is from the mobile terminal to the base station.
In the reverse transmission of user data in the mobile communication system as described above, the user data is transmitted at a rate of 0 kbps (i.e. no data to be transmitted), 9.6 kbps, 19.2 kbps, 38.4 kbps, 76.8 kbps or 153.6 kbps over a Reverse Traffic Channel (R-TRCH). The base station controls only the maximum allowable data rate of the R-TRCH, while the mobile terminal selects the actual data rate to use from among data rates that are less than the maximum allowable data rate. A Reverse Rate Indicator (RRI), which indicates a reverse data rate to be used by the mobile terminal, is reported to the base station over a Reverse Rate Indicator Channel (R-RICH).
FIG. 1 shows an exemplary structure of the R-RICH. As shown, an RRI of the R-RICH 110 is transmitted in the same time interval (or duration) as data traffic of a corresponding traffic channel 120 at time intervals of 26.67 ms. If a frame is defined as a data unit transmitted in each time interval, an RRI for a traffic channel carrying an i-th frame is transmitted in an i-th time interval. The RRI is composed of 3 bits, and the RRI's values are mapped to data rates as shown in the following table.
TABLE 1Data RateRRI   0 kbps000 9.6 kbps001 19.2 kbps010 38.4 kbps011 76.8 kbps100153.6 kbps101reserved110reserved111
In order to receive the i-th frame of the traffic channel, the base station first receives control information, which is transmitted over the R-RICH in the same time interval as the i-th frame (i.e. in the i-th time interval), and then performs channel decoding and de-spreading for the traffic channel.
FIG. 2 is a block diagram showing the configuration of a R-RICH transmitter for transmitting R-RICH signals from a mobile terminal in a mobile communication system. A Reverse Rate Indicator (RRI) symbol, composed of 3 bits, is transmitted at intervals of 16 slots.
As shown in FIG. 2, a simplex encoder 210 encodes 3-bit RRI symbols to output coded symbols. A codeword repeater 220 repeats the coded symbols in a predetermined repeated pattern (for example, a predetermined number of times). A puncturer 230 punctures the last 3 symbols of the repeated symbols from the repeater 220. A Time Division Multiplexer (TDM) 240 multiplexes the output of the puncturer 230 and a pilot-channel input sequence of all “0” symbols and outputs 128 binary symbols every slot. A signal point mapper 250 performs +1/−1 mapping (i.e., 0/1 →+1/−1) on the symbols output from the multiplexer 204. A Walsh spreader 260 spreads the output of the signal point mapper 250 by multiplying the output by predetermined Walsh codes for transmission over the R-RICH.
The R-RICH as shown in FIG. 1 and a traffic channel relating thereto receive the R-RICH signal transmitted by the transmitter as shown in FIG. 2, but can only decode the traffic channel signal only if there is no error in decoding the received R-RICH signal. If there is a decoding error of the R-RICH, the base station receiver cannot detect the actual data rate of the traffic channel, making error-free decoding difficult. Thus, it is very important for the 1×EVDO system to perform suitable power control to achieve a sufficiently-low reception error probability of the R-RICH since the reception performance of traffic signals is affected by the reception performance of the R-RICH signals.
Two types of power control are performed in the mobile communication system. The first type is inner loop power control, in which transmission power is controlled to allow the bit energy per noise ratio (Eb/Nt) of the R-RICH to approach a predetermined target setpoint. The second is outer loop power control, in which if an error has occurred in the received data, the target setpoint is increased; otherwise, the target setpoint is decreased.
However, the base station cannot determine whether there is an error in the decoded data received over the R-RICH, since additional information needed for determining whether there is an error in the decoded result is not transmitted from the mobile terminal over the R-RICH, as shown in FIG. 2. Thus, the mobile terminal must allocate sufficiently-high transmission power to the R-RICH, so that in any wireless environment the base station can receive the R-RICH signal with an error probability at a level lower than a predetermined limit value. However, such an increase in power increases interference with other channels.